Season-by-Season Guide: Should My Thermostat Be Set to Auto or Fan?

October 05, 2022

When the weather begins to cool off, you are probably wondering about how you’ll take full advantage of your heating and cooling. After all, HVAC costs frequently add up to a large portion of your monthly electric bill. To figure out new ways to lower their HVAC bill, some people look closely at their thermostat. Is there a setting they can use to improve efficiency?

Most thermostats include both a ‘Fan’ or ‘Fan On’ setting. But if the fan is going during a regular cycle, what does the fan setting provide for the HVAC system? This guide will help. We’ll share just what the fan setting is and how you can use it to reduce costs during the summer or winter.

What Is the Fan Setting on My Thermostat?

For the bulk of thermostats, the fan setting signifies that the air handler’s blower fan remains on. Certain furnaces will operate at a low level with this setting, but in most cases heating or cooling isn’t being generated. The ‘Auto’ setting, on the other hand, will start the fan during a heating or cooling cycle and turn it off once the cycle is complete.

There are advantages and disadvantages to trying the fan setting on your thermostat, and whether you do or don’t can depend on your unique comfort requirements.

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature in every room more uniform by allowing the fan to keep running.
  • Indoor air quality can increase since constant airflow will keep passing airborne pollutants into the air filter.
  • A smaller amount of start-stop cycles for the system's fan helps expand its life span. Because the air handler is often a component of the furnace, this means you could avoid needing furnace repair.

Disadvantages to using the Fan/On setting:

  • A constant fan will likely add to your energy costs slightly.
  • Nonstop airflow may clog your air filter up more quickly, increasing the frequency you’ll need to replace it.

Should My Thermostat Be on Fan or Auto in Summer/Winter

In the summer, warm air can persist in unfinished spaces like the attic or an attached garage. If you keep the fan running, your HVAC system can draw this warm air into the rest of your home, forcing the HVAC system to run longer to keep up with the set temperature. In serious heat, this may result in needing AC repair more quickly as wear and tear increases.

The opposite can occur over the winter. Cooler spaces like a basement will hold onto cooler air, which will eventually make its way into the rest of your home. Leaving the fan running may pull more cold air upward, increasing the amount of heating you need to stay warm.

If you’re still trying to determine if you should switch to the fan/on setting, remember that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on may be ideal for you if:

Someone in your household has allergies. Allergies and other respiratory conditions can be stressful on the family. Leaving the fan on should help to improve indoor air quality, helping your family breathe easier.

Your home deals with hot and cold spots. Lots of homes deal with difficult hot and cold spots that quickly return to a temperature different from the rest of the house. The fan setting can help limit these changes by steadily refreshing each room’s airflow.